1 Roswell, 1947

Alien autopsy? A still from the documentary The Roswell Incident Photograph: Channel 4

Conspiracy theorists claimed the US military had captured a crashed alien aircraft, but "The Man" maintained it had merely recovered debris from a top secret surveillance balloon. Ask Ant & Dec – they made a film about it: 2006 flop Alien Autopsy.

2 Belgian wave, 1989-90

A sighting from the Belgian UFO wave (29 November 1989 to April 1990).

Over five months, 13,500 people claimed to have witnessed large, silent, low-flying black triangles, and around 2,600 of them filed written statements. Sceptics blame helicopters or mass delusions caused by eating chips with mayonnaise.

4 Kenneth Arnold case, 1947

Pilots EJ Smith, Kenneth Arnold, and Ralph E Stevens look at a photo of a UFO that they spotted in Washington. Photograph: Bettmann/Corbis

The press first coined the term "flying saucer" after this Idaho pilot claimed he had seen a string of nine shiny, saucer-shaped objects flying at supersonic speeds near Mount Rainier, Washington. What's the frequency, Kenneth?

6 Ronald Reagan, 1974

Presidents Jimmy Carter and Ronald Regan both claim to have seen UFOs. Carter was widely mocked for his 1973 sighting, but the man who eventually succeeded him in the White House also saw a mysterious object – in 1974 above Petersfield, California. Probably wisely, the wily old cowboy kept pretty quiet about it.

7 Levelland case, 1957

Reports of a UFO sighting in Levelland, Texas in 1957. Photograph: guardian.co.uk

Texas motorists reported their engines stalling after encountering a glowing, egg-shaped object – and that their vehicles restarted after it flew past. An investigation concluded that it was down to an electrical storm and "ball lightning".

10 Tehran incident, 1976

US military report into a sighting of a UFO over Tehran in 1976.

A UFO allegedly whizzed over Iran's capital, disabling the electronic instrumentation of two F-4 Phantom II jets and jamming ground control equipment. Iranian generals said on record that they thought the object was extra-terrestrial. Don't tell Melanie Phillips.